Isotopes
•
These are atoms of element with the same atomic number but different number of
neutrons.
•
They therefore have different mass number.
•
Examples of isotopes: Hydrogen, Lithium, chlorine.
Hydrogen has three isotopes e.g.
1
2
3
• H-1, H-2, H-3;
1H, 1H, 1H;
Lithium has two isotopes
• Li – 6, Li – 7;
Chlorine has two isotopes
• Cl -35, Cl – 37;
6
3Li,
7
35
37
17Cl, 17
3Li;
Cl
HOW COMPOUNDS ARE FORMED
•
A compound is a pure substance made up of two or more elements that are
chemically combined.
•
Examples Water (H2O) & hydrogen peroxide (H2O2)
•
There are two types of compounds
•
Ionic compounds & molecular compounds
IONIC COMPOUND
•
Ionic compounds are pure substances usually consisting of at least one metal and
one non-metal.
•
example sodium chloride, NaCl
•
All ionic compound have high melting point
•
When they dissolve in water, the solution formed can conduct electricity.
•
The solution is called electrolyte
Valence electrons
Electrons occupy more than 99.99% of an atom’s volume.
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• Electrons can move between energy levels.
• The outermost shell that has electrons in it is called the valence shell.
•
Electrons in this shell are called valence electrons
•
Other shells containing electrons are called inner shells.
•
the electrons in them are called inner electrons.
•
The properties of elements are strongly affected by their valence electrons.
•
Other shells containing electrons are called inner shells.
•
the electrons in them are called inner electrons.
•
The properties of elements are strongly affected by their valence electrons.
Some Elements in the periodic table showing valence Electrons
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Forming Ionic Compounds
•
While combining, each atom changes into an ion.
•
Ions are formed when one or more electrons move from a metal atom over to a
nonmetal atom.
•
a sodium atom loses an electron by giving it to a chlorine atom.
•
This produces a positive sodium ion and a negative chloride ion.
•
Positive and negative ions attract each other, so in an ionic compound, all the
positive ions are attracted to all the negative ions.
•
A connection between atoms or ions is known as a bond.
•
The attractions between ions are called ionic bonds
Ionic Compounds
Names and Formulas of Common Compounds
Common Names
Drawing chalk
Chemical Names
calcium sulphate
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antacid chalk
calcium carbonate
Naming Salts
• In chemistry “salt” does not indicate which specific
elements are found within a compound e.g.
table salt
Road salt
sodium chloride.
calcium chloride
Clockwise from the lower left, the salts shown here are sodium chloride, ron(II) sulphate,
iron(III) sulphate, copper(II) sulphate, and copper (II) carbonate
Chemical Names and formula
•
Every compound has a chemical name and formula
•
For any element to form an ionic compound, it has to form an ion
Ionic Charges
Element
Hydrogen
lithium
nitrogen
oxygen
Magnesium
Aluminum
Iron*
Copper*
Lead*
Ion Charge
1+
1+
3–
2–
2+
3+
2+ or 3+
1+ or 2+
2+ or 4+
Ion Notation
H+
Li+
N3–
O2–
Mg2+
Al3+
2+
Fe or Fe3+
Cu+ or Cu2+
Pb2+ or Pb4+
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Ion Name
hydrogen
lithium
nitride
oxide
magnesium
aluminum
iron(II) or iron(III)
copper(I) or copper(II)
lead(II) or lead(IV)
Naming Ionic Compounds
1. Name the metal ion first.
2. If the element can form an ion in more than one way, include a Roman numeral to
indicate the charge
3. Name the non-metal ion second.
4. When a non-metal becomes a negative ion, the ending of its name changes to “ide.”
5. The name for an ionic compound is a combination of the ion names of the
elements.
• The name of NaCl is, therefore, sodium chloride.
•
• Examples:
• Positive Ion
Negative Ion Formula Name
2+
•
Mg
O2–
MgO
•
Ba2+
F–
•
K+
N3–
•
Pb2+
Cl-
•
Pb4+
N3-
Molecular Compounds
•
When non-metals combine, a pure substance called a molecular compound is
formed.
•
In molecular compounds, the atoms share electrons to form small groups, called
molecules.
•
Molecular Compounds :
 can be solids, liquids, or gases at room temperature
 are usually good insulators but poor conductors of electricity
 have relatively low boiling points
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Naming Molecular compounds
•
•
•
In naming molecular compounds, prefixes are used.
Prefixes indicate the number of atoms present in the molecule
E.g. Number of atoms Prefix
1
mono2
di3
tri4
tetra5
penta-
Steps for naming molecular compounds
1. Examine the formula given
N2O
PBr3
CS2
2. Name the first element
Nitrogen
phosphorus
Carbon
3. Name the second element and add –ide
oxide
bromide
sulphide
•
Add prefixes indicating the number of atoms of each
•
Dinitrogen monoxide; phosphorus tribromide; carbon disulphide
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